Since signing up for AdSense I have been curious is the AdSense page impressions are a more accurate count of unique visits to a website than those generated from an analysis of webserver logs? I know they miss people who use Firefox and who block AdSense. I am guessing they also miss or ignore most of the crawlers.
well firstly those are page views and not unique visitors also, if you niche does not have enough ads in the inventory, ads will show up as psa's and do not count in stats. As a matter of fact it would be pure genius to derrive correlation between AdSense page imressions and unique visitors.
The only thing that AdSense page impressions tell you is how many times google ads where displayed on your pages. You can't use it as a basis of how many page views your server is serving. Although, I do use it as a quick general gauge of how my site is growing over time.